If I have read your post correctly, you are trying to re-assign the dynamic-vpn HTTPS port (TCP 443) to a different port, so you can use Exchange OWA? I am guessing that you have a single IP address. If so, then you have a bit of a problem.
You can change the HTTP/HTTPS port for the web interface, but it does not change the inbound services port on your WAN interface.
at-2/0/0.0 {
host-inbound-traffic {
system-services {
https;
ike;
}
}
}
I suggest setting up a destination NAT rule for the OWA traffic and from WAN TCP 444 to LAN TCP 443.
If you have more than one WAN IP address then it is easy to fix.